In the long-term, herbivores can alter nutrient dynamics in tundra ecosystems by changing the functional composition of the vegetation. Yet, herbivores may also alter nutrient dynamics by modifying plant-community nutrient levels, and these changes are likely to happen much faster than structural changes. Here, by using novel Near Infrared-Reflectance Spectroscopy (NIRS) methodology, we quantified the effects of small rodents and reindeer on tundra-grassland plant-community nitrogen and phosphorus levels throughout a single growing season. Herbivores were immediate, positive modifiers of plant-community nutrient levels. Plant-community nutrient contents in herbivore-affected tundra were still much higher in senescent leaves at the end of the summer, suggesting that herbivory is accelerating short-term tundra-grassland nutrient dynamics. Overall, our findings from tundra-grasslands align with theoretical expectations of positive herbivore effects on nutrient cycling in relatively productive ecosystems, when dominant, nutrient-rich growth forms benefit from herbivory.
Reference: Petit Bon, M., Inga, K. G., Jónsdóttir, I. S., Utsi, T. A., Soininen, E. M., & Bråthen, K. A. (2020). Interactions between winter and summer herbivory affect spatial and temporal plant nutrient dynamics in tundra grassland communities. Oikos. https://doi.org/10.1111/oik.07074
Picture: experimental sites at Ifjordfellet, Finnmark, northern Norway (photo: Matteo Petit Bon)